1. Field of the Invention
The present invention is directed to a reciprocatory dry shaver having a movable cutter which is driven to reciprocate by a permanent magnet linear motor.
2. Description of the Prior Art
European Patent Publication EP 349077 discloses a reciprocatory dry shaver comprising a linear motor for reciprocating a movable critter in shearing engagement with a stationary cutter. The motor comprises an electromagnet as a stator and a permanent magnet as a reciprocator supporting a movable cutter. The electromagnet is energized by a current of a fixed frequency to drive the reciprocator and the movable cutter. When the movable cutter experiences a heavy load during the shaving, the movable cutter moves only by a slight stroke, which reduces an oscillation amplitude with an attendant decrease in the speed of the movable cutter, thereby reducing cutting sharpness and even failing to cut the hairs. There have been also known in the art reciprocatory shavers with a feedback control of a motor, as disclosed in Japanese Patent Early Publication No. 5-38387, Japanese Utility Model Early Publication No. 62-23569, and Japanese Utility Model Early Publication No. 61-167174. The shavers of these prior art includes a rotary motor and a reciprocator carrying a movable cutter. The reciprocator is coupled to the rotary motor through a rotary-to-reciprocation conversion mechanism so as to be driven by the motor to reciprocate. A detector is provided in the shavers to detect a motor current, motor speed, or speed of the reciprocator to give a corresponding output which is processed in a feedback manner to vary the motor output in an attempt to keep a constant amplitude of oscillation. However, due to the inclusion of the rotary-to-reciprocation conversion mechanism in which energy loss is inherent, there is always response delay in the feedback control. Because of difficulty of effecting quick control, the movable cutter encountering a heavy lead during the shaving can be driven to move with a stronger force than earlier only after some delay, thus failing to achieve an immediate sharp cut.